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| author | Joachim Breitner <mail@joachim-breitner.de> | 2017-03-09 16:13:08 +0100 |
|---|---|---|
| committer | Joachim Breitner <mail@joachim-breitner.de> | 2017-03-09 16:13:08 +0100 |
| commit | 665cefe80d112ed2e4fb9617d277a1466e83f9bd (patch) | |
| tree | 0d68b9253c0467f3a0a072cec3b42bfcc9a48611 /libraries/base/GHC/Base.hs | |
| parent | 3b40450436db1c927d88dbe7c6bad33f35dd4b1a (diff) | |
| download | haskell-665cefe80d112ed2e4fb9617d277a1466e83f9bd.tar.gz | |
Add a comment to the mapFB rules
to amend 2fa44217c1d9722227297eefb0d6c6aed7e128ca.
Diffstat (limited to 'libraries/base/GHC/Base.hs')
| -rw-r--r-- | libraries/base/GHC/Base.hs | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs index 6f9d45469f..a678c22bbf 100644 --- a/libraries/base/GHC/Base.hs +++ b/libraries/base/GHC/Base.hs @@ -964,10 +964,12 @@ mapFB c f = \x ys -> c (f x) ys -- (along with build's unfolding) else we'd get an infinite loop -- in the rules. Hence the activation control below. -- --- The "mapFB" rule optimises compositions of map. --- -- This same pattern is followed by many other functions: -- e.g. append, filter, iterate, repeat, etc. +-- +-- The "mapFB" rule optimises compositions of map and +-- the "mapFB/id" rule get rids of 'map id' calls. +-- (Any similarity to the Functor laws for [] is expected.) {-# RULES "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs) |